The present invention relates to a temperature sensor element and a temperature sensor including the same. More specifically the present invention pertains to a temperature sensor with excellent heat resistance, heat response, and reliability.
With enhanced concern about the environment, it is required to treat the gaseous exhaust from an engine of an automobile before release to the atmosphere. A catalytic converter is accordingly arranged in the exhaust system for converting the gaseous exhaust to a harmless form. Accurate measurement of the catalyst temperature is essential for enhancing the efficiency of conversion, that is, the catalyst performance. A temperature sensor element used for that purpose should have excellent heat resistance, quick heat response, and high reliability with a less variation in resistance against time.
One of known temperature sensor elements has structure shown in FIG. 16. A temperature sensor element 200 includes a sintered heat sensitive body 201 of a linear type, non-linear type, negative temperature coefficient type, or positive temperature coefficient type and a pair of lead wires 202 of a noble metal, which are integrated with the heat sensitive body 201. The temperature sensor element 200 is manufactured by preliminarily firing a material mixture of a predetermined composition, grinding the fired mixture to powder, molding the power to a predetermined form, inserting the noble-metal lead wires 202 into the molded body, and firing the molded body at a high temperature of not lower than 1600.degree. C.
FIG. 17 shows structure of a temperature sensor including the temperature sensor element 200 thus obtained. A pair of lead wires 203 connecting with the noble-metal lead wires 202 of the temperature sensor element 200 are fixed to an electrical insulator 204 in a metal housing 205. A heat-resistant metal cap 208 for covering the temperature sensor element 200 is welded to one end of the housing 205, whereas a metal flange 206 for fixing the temperature sensor to an object of temperature measurement is fixed to the other end of the housing 205. An electrical insulator 207 insulates the lead wires 203 from the housing 205 and the flange 206 (see, for example, Japanese Laid-Open Patent Hei 6-283310).
This prior art temperature sensor including the temperature sensor element has a problem of poor heat response when being applied to the catalytic converter of the automobile. The poor heat response is ascribed to the fact that the heat sensitive body 201, which is a sintered, powder-molded body, is rather bulky and has a high heat capacity and that the temperature sensor element 200 is covered with the heat-resistant cap 208. Removal of the heat-resistant metal cap 208 from the prior art temperature sensor causes another problem; that is, carbon in the gaseous exhaust deposits between the pair of lead wires 202 and causes a short circuit between the lead wires 202.